Nowadays, high power converter apparatus may employ two or more resonant converters connected in parallel to deliver high output current, which has advantages for maintenance, and the reliability of the apparatus may be improved by using parallel redundancy. Although a plurality of resonant converters connected in parallel may output the same current by using the symmetrical layout, it is difficult to obtain a completely symmetrical layout because there are some inherent differences between circuit layouts, and thus there is always current difference between the converters. It results in low efficiency and thermal loss of the apparatus, and the loss for the converter outputting high current may be large. The inventors hereof have recognized a need for a scheme keeping the balance of the output currents of the plurality of resonant converters connected in parallel.